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circulator

A three- or four-port electronic device in which signals entering port number 1 appear only at port number 2, while signals entering port number 2 emerge only at port number 3, and so on. It is used, for example, in a radio telescope employing a negative-resistance preamplifier, such as a parametric amplifier or a maser amplifier; the circulator isolates the preamplifier from the antenna, which, if connected directly, might oscillate.

Circulator

 

(also microwave circulator), a multiarm—that is, multiport—device for transmitting the power of high-frequency electromagnetic oscillations, usually microwaves, in a particular direction. The power that enters one of the ports is transmitted to another, strictly specified port in sequence. Circulators are classified as electronic and ferrite.

Electronic circulators make use of the ability of certain phase shifters to produce a nonreciprocal phase shift of π radians (see alsoPHASE INVERTER). Such circulators consists of discrete components, for example, transistors, diodes, or resistors. Three-port Y-shaped electronic circulators have lumped elements and are used in the frequency band from less than ten to several tens of megahertz.

The operation of ferrite circulators is based on the ability of ferrites that are magnetized in a constant applied magnetic field to produce—when they interact with an electromagnetic field or wave—a nonreciprocal phase shift, a nonreciprocal rotation of the plane of polarization (seeFARAD AY EFFECT), or a combination of waves such that the waves propagate in only one arm of the circulator. Several different types of ferrite circulators are distinguished. Phase-shift Y circulators have lumped elements and are used in the frequency band from hundreds to thousands of megahertz; in this type of circulator, the nonreciprocal phase shift is achieved by means of a magnetized ferrite rod or cylinder and a system of inductively coupled windings. Other types of ferrite circulators are based on junctions of rectangular or circular wave guides or on strip transmission lines, including microstrip lines. Such circulators may be Y-, T-, or X-shaped; they have distributed elements and are used in the frequency band from thousands to tens of thousands of megahertz. The X-shaped circulators are usually called four-port circulators. Examples of waveguide circulators include the four-port circulator known as a polarization rotator (see Figure 1) and the phase-shift circulator, which consists of two wave-guide bridges and two nonreciprocal ferrite phase shifters.

Figure 1. Polarization rotator based on a circular wave-guide section: (1), (2), (3), and (4) circulator ports, which are conventional rectangular wave-guide sections positioned in sequence at an angle of 45° with respect to the preceding port. The broken line represents the ferrite, which rotates the wave’s plane of polarization by 45° in the direction indicated by the arrow. As a result of the rotation, power entering port (4) is transmitted only to port (1), power entering port (3) is transmitted only to port (4), and so forth.

Ferrite circulators are the most promising. For example, they are used as switches, since the port sequence is reversed whenever the direction of the constant magnetic field is changed. In antenna feed lines, four-port and Y ferrite circulators are employed to switch an antenna or a phased-array module from the transmitting mode to the receiving mode. Y ferrite circulators in which one arm contains an absorbing load are used as electric valves. If several Y circulators are connected in series, a circulator array with any desired number of arms may be obtained. In conjunction with bandpass filters, circulator arrays make it possible to construct devices for the combination or separation of signals with different carrier frequencies; such devices require a minimum number of filters.

REFERENCES

Lebedev, I. V. Tekhnika i pribory SVCh, 2nd ed., vol. 1. Moscow, 1970.
Vol’man, V. I., and Iu. V. Pimenov. Tekhnicheskaia elektrodinamika. Moscow, 1971.
Knerr, R. H. “An Annotated Bibliography of Microwave Circulators and Isolators, 1968–1975.” IEEE Transactions on Microwave Theory and Techniques, 1975, vol. 23, no. 10 (October).

R. I. PERETS

circulator

[‚sər·kyə·′lād·ər]
(electromagnetism)
A waveguide component having a number of terminals so arranged that energy entering one terminal is transmitted to the next adjacent terminal in a particular direction. Also known as microwave circulator.
References in classic literature ?
as of an intellect doubled on itself), by abandonment to the nature of things; that beside his privacy of power as an individual man, there is a great public power on which he can draw, by unlocking, at all risks, his human doors, and suffering the ethereal tides to roll and circulate through him; then he is caught up into the life of the Universe, his speech is thunder, his thought is law, and his words are universally intelligible as the plants and animals.
The roofing of this abode did not rest directly upon the walls, and the air could, therefore, circulate freely, but windows there were none, and the door hardly deserved the name.
The presence of this extraordinary being caused, as it were, a breath of life to circulate throughout the entire cathedral.
A strange rumour began to circulate, meanwhile; no less than that the respectable and highly respected General Epanchin was himself so fascinated by Nastasia Philipovna that his feeling for her amounted almost to passion.
Let me circulate my blood and rouse my ingenuity, by taking to the road again.
The previous evening each furnace had been charged with 114,000 pounds weight of metal in bars disposed cross-ways to each other, so as to allow the hot air to circulate freely between them.
It is not enough that a country should lose none of the money that forms its capital; you will not increase its prosperity by more or less ingenious devices for causing this amount to circulate, by means of production and consumption, through the greatest possible number of hands.
My residence was more favorable, not only to thought, but to serious reading, than a university; and though I was beyond the range of the ordinary circulating library, I had more than ever come within the influence of those books which circulate round the world, whose sentences were first written on bark, and are now merely copied from time to time on to linen paper.
Your name shall circulate with renown all round the earth, like unto the ship that was to have sailed from Corsor; and in Roeskilde--"
Poor little Rosa put a forefinger into each of her ears when these rumours began to circulate, and retired into a corner, beseeching not to be told any more; but Miss Landless, begging permission of Miss Twinkleton to go and speak with her brother, and pretty plainly showing that she would take it if it were not given, struck out the more definite course of going to Mr.
Every word this creature said was a cordial to me, and put new life and new spirit into my heart; my blood began to circulate immediately, and I was quite another body; I ate my victuals again, and grew better presently after it.
Suffer THAT to circulate, let your spirits be never so stagnant.